Stock feed system for a multi-layer headbox and method in the operation of a multi-layer headbox

Abstract: The invention concerns a stock feed system for a multi-layer headbox (10) and a method in the operation of a multi-layer headbox. According to the invention, into each inlet header (11,12,13) of the multi-layer headbox (10), a stock concept (M₁, M₂...) is passed which has been produced out of the same fresh stock (M) by to the fresh stock adding the necessary chemicals and fillers.

Description: The invention concerns a stock feed system for a multi-layer headbox and a method in the operation of a multi-layer headbox. In the prior art (US-A-4 021 295), systems for the operation of multi-layer headboxes are known in which there are separate fresh stocks for the surface layers and for the middle layers. Thus, in the prior-art systems, there have been at least double fresh-stock systems for the formation of the layers. In the solutions of equipment, the stocks introduced along separate fresh-stock lines have been processed in vortex cleaning and in de-aeration tanks, and in the system, into said at least two fresh-stock lines, feeds of fillers or starch complying with the required paper grade have been passed. In the present application, it is suggested that, in a paper machine that comprises a multi-layer headbox and therein at least two separate inlet headers or equivalent, for the inlet headers, separate stocks are prepared out of the same fresh stock and from the same stock tank. According to the invention, the fresh stock passed out of the stock tank is divided into two or more component flows. Into said component flows to be fed into the multi-layer headbox, the chemicals and/or additives purposeful for the quality or the economy of production of different paper grades are passed. The stock system in accordance with the invention for a multi-layer headbox is mainly characterized in that, into each inlet header of the multi-layer headbox, a stock concept is passed which has been produced out of the same fresh stock by to the fresh stock adding the necessary chemicals and fillers. The method in accordance with the invention is mainly characterized in that, in the method, the stock for each header is prepared out of one and the same fresh stock by to said fresh stock adding the necessary chemicals and fillers. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawing, the invention being, yet, not supposed to be confined to said embodiments alone. Figure 1 shows a first preferred embodiment of the invention, in which the stock flow passed out of the fresh-stock tank is divided into three component flows, which are passed further, after feeds of chemicals and fillers, into the different inlet headers in the multi-layer headbox. Figure 2 shows a second preferred embodiment of the stock feed system in accordance with the invention for a multi-layer headbox. Fig. 1 is a schematic illustration of a first preferred embodiment of the invention, which is favourably suitable for SC-paper. As is shown in the figure, the multi-layer headbox 10 comprises three inlet headers, i.e. the inlet headers 11,12 and 13. From the inlet header 11, the stock is passed through the distribution manifold 14a 1.1 , 14a 1.2 ... to the turbulence generator 15 into its turbulence tubes 15a 1.1 ,15a 1.2 ... and further into the slice cone 16. From the inlet header 12, the stock M 2 is passed through the distribution pipes 14a 2.1 ,14a 2.2 ... of the distributor manifold 14 to the turbulence generator 15 into its turbulence tubes 15a 2.1 ,15a 2.2 ..., further into the slice cone 16, and from the inlet header 13 the stock M 3 is passed through the distribution pipes 14a 3.1 ,14a 3.2 ... of the distributor manifold 14 to the turbulence generator 15 into its turbulence tubes 15a 3.1 ,15a 3.2 ... and further into the slice cone 16. Thus, by means of the multi-layer headbox shown in Fig. 1, the paper is formed out of three stock concepts M 1 ,M 2 and M 3 . Thus, the web will comprise three layers formed out of different stock concepts. It is an essential feature of the solution of the present invention that the equipment comprises a single stock system, the stocks M 1 ,M 2 and M 3 being formed out of the same fresh stock M. While there were several fresh-stock lines in the prior-art solutions, in the method and the solution of equipment in accordance with the present invention, different layers are formed out of the same fresh stock M, which is passed out of the same fresh-stock tank 17. In the way that is shown in Fig. 1, the fresh stock M is passed out of the fresh-stock tank 17 along the line 18a and is branched at the branching point P 1 into two branch lines 18a 2 and 18a 3 . In the embodiment of Fig. 1, in the branch line 18a 2 the chemical 3a is added to the stock M, and in the branch line 18a 3 the chemical 3b, such as a filler or starch, is added. In the lines 18a 2 ,18a 3 , the stocks are made to flow further by means of the pumps 19a 1 and 19a 2 so that, along the line 18a 2 , the stock is passed into the machine screen 20a 1 . The retention agent 5b is fed into the stock before the machine screen 20a 1 , and the retention agent 5bb after the machine screen. In this way, good mixing of the retention agent and the stock is achieved. Along the line 21a 1 , the stock M 2 that was formed is passed into the middle inlet header 12 of the multi-layer headbox. From the line 18a 2 after the pump 19a 1 , from the branch point C, the line 18a 2.1 passes to the machine screen 20a 2 , and from the machine screen 20a 2 the line 21a 2 passes to the multi-layer headbox. At the front side of the machine screen 20a 2 , the retention agent 5a is fed into the line 18a 2.1 , and after the machine screen 20a 2 the retention agent 5aa is fed into the line 21a 2 . Along the line 21a 2 the stock flow M 3 is passed into the inlet header 13 of the multi-layer headbox. From the branch point C, the line 18a 2.2 passes to the machine screen 20a 3 and further into the multi-layer headbox. Into the line 18a 2.2 , before the machine screen 20a 3 , the retention agent 5c is fed, and after the machine screen 20a 3 the retention agent 5cc is fed. Along the line 21a 3 , the stock flow M 1 is passed into the inlet header 11 of the multi-layer headbox. Fig. 2 shows an embodiment of the invention in which one unified stock flow M is passed out of the stock tank 17 along the line 22a 1 to the branch point D 1 . After the branch point D 1 , the chemical 3a' is added to the fresh stock M into the line 220a 1 . By means of the pump 19a 1 ' the stock is made to flow further into the machine screen 23a 1 , and before the machine screen 23a 1 , the retention agent 5a' is added, and after the machine screen 23a 1 the retention agent 5aa'. The stock M 3 ' flow is passed along the line 24a 1 into the inlet header 13 of the multi-layer headbox. From the branch point D 1 the stock M is made to flow along the line 22a 1 to the branch point D 2 , from which the stock M is branched into the lines 220a 2 and 220a 3 . Into the line 220a 2 the chemical 3b', such as filler or starch, is added into the stock M before the pump 19a 2 '. By means of the pump 19a 2 ' said concept is passed further into the machine screen 23a 2 . Before the machine screen 23a 2 the retention agent 5b', such as some suitable chemical, is added to the stock, and after the machine screen 23a 2 the retention agent 5bb'. The stock concept M 2 ' produced in this way is passed further along the line 24a 2 into the multi-layer headbox, into its middle inlet header 12. Similarly, from the branch point D 2 the stock M is passed along the line 220a 3 , after the feed of chemical 3c', by means of the circulation produced by the pump 19a 3 ', into the machine screen 23a 3 , before which the retention agent 5c' is added, and after which the retention agent 5cc' is added, and the concept M 1 ' thereby produced is passed further along the line 24a 3 into the inlet header 11 of the multi-layer headbox 10. Thus, in the concept in accordance with the invention, just a single circulation of stock is used, in which there is just one starting fresh stock M. Said fresh stock M is processed further by to it adding chemicals and fillers, whereby out of one fresh stock M all the necessary different stock concepts M 1 ,M 2 and M 3 are obtained for the inlet headers 11,12 and 13 of the multi-layer headbox. The invention concerns a stock feed system for a multi-layer headbox (10) and a method in the operation of a multi-layer headbox. According to the invention, into each inlet header (11,12,13) of the multi-layer headbox (10), a stock concept (M 1 , M 2 ...) is passed which has been produced out of the same fresh stock (M) by to the fresh stock adding the necessary chemicals and fillers.

Claims: Stock feed system for a multi-layer headbox (10) for forming multi-ply paper, wherein into each inlet header (11, 12, 13) of the multi-layer headbox (10) different stock concepts (M 1 , M 2 ,...) are passed, characterized in that the stock concepts (M 1 , M 2 , ...) for every ply are produced out of the same fresh stock (M) from a common stock tank (17) by adding the necessary chemicals and fillers to the fresh stock (M) after said fresh stock is divided into separate stock flows. Stock feed system as claimed in claim 1, characterized in that the system comprises a fresh stock line (18al; 22al) from said common stock tank, which line is branched into different lines in accordance with the requirements of each particular concept. Method of operating a multi-layer headbox (10) for forming multi-ply paper, wherein into each of at least two inlet headers (11, 12, ...) different stock concepts (M 1 , M 2 ; M', M") are passed and the stock being made to flow out of said inlet headers (11, 12,..) and further brought to a system of distributor pipes into a turbulence generator and further into the slice cone (16), characterized in that the stock concepts (M 1 , M2,...) for every ply are produced out of the same fresh stock (M) from a common stock tank (17) by adding the necessary chemicals and fillers to the fresh stock (M) after said fresh stock is divided into separate stock flows. Method as claimed in claim 3, characterized in that the fresh stock (M) is made to flow through branch points into different lines, a chemical being fed into each of said lines in accordance with the requirements of the particular stock concept to be fed into the inlet header of the multi-layer headbox.

Inventors: HUOVILA JYRKI, ILMONIEMI ERKKI, ODELL MICHAEL, SUONPERAE ANTTI, HUOVILA, JYRKI, ILMONIEMI, ERKKI, ODELL, MICHAEL, SUONPERAE, ANTTI, Suonperä, Antti
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21F9
IPC codes: D21F11, D21F9